6,022 research outputs found
Systematic Effects in Interferometric Observations of the CMB Polarization
Get PDFThe detection of the primordial -mode spectrum of the polarized cosmic
microwave background (CMB) signal may provide a probe of inflation. However,
observation of such a faint signal requires excellent control of systematic
errors. Interferometry proves to be a promising approach for overcoming such a
challenge. In this paper we present a complete simulation pipeline of
interferometric observations of CMB polarization, including systematic errors.
We employ two different methods for obtaining the power spectra from mock data
produced by simulated observations: the maximum likelihood method and the
method of Gibbs sampling. We show that the results from both methods are
consistent with each other, as well as, within a factor of 6, with analytical
estimates. Several categories of systematic errors are considered: instrumental
errors, consisting of antenna gain and antenna coupling errors, and beam
errors, consisting of antenna pointing errors, beam cross-polarization and beam
shape (and size) errors. In order to recover the tensor-to-scalar ratio, ,
within a 10% tolerance level, which ensures the experiment is sensitive enough
to detect the -signal at in the multipole range ,
we find that, for a QUBIC-like experiment, Gaussian-distributed systematic
errors must be controlled with precisions of for antenna
gain, for antenna coupling, for pointing, for beam
shape, and for beam cross-polarization.Comment: 15 pages, 6 figures, submitted to ApJ
Bayesian Inference of Polarized CMB Power Spectra from Interferometric Data
Get PDFDetection of B-mode polarization of the cosmic microwave background (CMB)
radiation is one of the frontiers of observational cosmology. Because they are
an order of magnitude fainter than E-modes, it is quite a challenge to detect
B-modes. Having more manageable systematics, interferometers prove to have a
substantial advantage over imagers in detecting such faint signals. Here, we
present a method for Bayesian inference of power spectra and signal
reconstruction from interferometric data of the CMB polarization signal by
using the technique of Gibbs sampling. We demonstrate the validity of the
method in the flat-sky approximation for a simulation of an interferometric
observation on a finite patch with incomplete uv-plane coverage, a finite beam
size and a realistic noise model. With a computational complexity of
O(n^{3/2}), n being the data size, Gibbs sampling provides an efficient method
for analyzing upcoming cosmology observations.Comment: 8 pages, 8 figures, expanded discussion and edited to match ApJS
approved version, acknowledgments update
Bayesian semi-blind component separation for foreground removal in interferometric 21-cm observations
Full text linkWe present in this paper a new Bayesian semi-blind approach for foreground
removal in observations of the 21-cm signal with interferometers. The
technique, which we call HIEMICA (HI Expectation-Maximization Independent
Component Analysis), is an extension of the Independent Component Analysis
(ICA) technique developed for two-dimensional (2D) CMB maps to
three-dimensional (3D) 21-cm cosmological signals measured by interferometers.
This technique provides a fully Bayesian inference of power spectra and maps
and separates the foregrounds from signal based on the diversity of their power
spectra. Only relying on the statistical independence of the components, this
approach can jointly estimate the 3D power spectrum of the 21-cm signal and,
the 2D angular power spectrum and the frequency dependence of each foreground
component, without any prior assumptions about foregrounds. This approach has
been tested extensively by applying it to mock data from interferometric 21-cm
intensity mapping observations under idealized assumptions of instrumental
effects. We also discuss the impact when the noise properties are not known
completely. As a first step toward solving the 21 cm power spectrum analysis
problem we compare the semi-blind HIEMICA technique with the commonly used
Principal Component Analysis (PCA). Under the same idealized circumstances the
proposed technique provides significantly improved recovery of the power
spectrum. This technique can be applied straightforwardly to all 21-cm
interferometric observations, including epoch of reionization measurements, and
can be extended to single-dish observations as well.Comment: 18 pages, 7 figures, added some discussions about the impact of noise
misspecificatio
Appeal No. 0823: Ohio Valley Energy Systems Corp. v. Division of Oil & Gas Resources Management
Get PDFChief\u27s April 21, 2010 Letter (Adams/Balough water supply
Solving Linux Upgradeability Problems Using Boolean Optimization
Full text linkManaging the software complexity of package-based systems can be regarded as
one of the main challenges in software architectures. Upgrades are required on
a short time basis and systems are expected to be reliable and consistent after
that. For each package in the system, a set of dependencies and a set of
conflicts have to be taken into account. Although this problem is
computationally hard to solve, efficient tools are required. In the best
scenario, the solutions provided should also be optimal in order to better
fulfill users requirements and expectations. This paper describes two different
tools, both based on Boolean satisfiability (SAT), for solving Linux
upgradeability problems. The problem instances used in the evaluation of these
tools were mainly obtained from real environments, and are subject to two
different lexicographic optimization criteria. The developed tools can provide
optimal solutions for many of the instances, but a few challenges remain.
Moreover, it is our understanding that this problem has many similarities with
other configuration problems, and therefore the same techniques can be used in
other domains.Comment: In Proceedings LoCoCo 2010, arXiv:1007.083
Electrospinning of 2-hydroxypropyl-β-cyclodextrin aqueous solutions with added salts
Get PDFIt has been proposed that hydrogen bonding plays a role in promoting the electrospinnability of some materials. In this study, the role of non-covalent interactions in the electrospinnability of 2-hydroxypropyl-β-cyclodextrin (2HP-β-CD) was investigated by varying the physical-chemical properties the solvents. The rheological behaviour of a peroxide-aqueous/acetone-ethanol/NaHCO3 solution and an aqueous urea solution, as a function of aqueous 2HP-β-CD concentration, was compared. The rheological behaviour of 2HP-β-CD solutions was characterized by a frequency-independent stress relaxation plateau such as that observed in cross-linked polymer networks and reversible polymer gels with non-linear viscoelasticity. We conclude that the electrospinnability of 2HP-β-CD is, as evidenced by the changes in the morphology of the electrospun 2HP-β-CD materials, in agreement with other related studies on the electrospinning of Cyclodextrins. Also, the electrospinnability of 2HP-β-CD does appear to be related to the physical-chemical properties of the solvent systems
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